MAX109
Internal Reference
The MAX109 features an on-chip 2.5V precision
bandgap reference used to generate the full-scale
range for the data converter. Connecting REFIN with
REFOUT applies the reference output to the positive
input of the reference buffer. The buffer’s negative input
is internally connected to GNDR. It is recommended
that GNDR be connected to GNDI on the user’s appli-
cation board.
If required, REFOUT can source up to 2.5mA to supply
other external devices. Additionally, an adjustable
external reference can be used to adjust the ADC’s full-
scale range. To use an external reference supply, con-
nect a high-precision bandgap reference to the REFIN
pin and leave the REFOUT pin floating. REFIN has a
typical input resistance R
REFIN
of 5kΩ and accepts
input voltages of 2.5V ±10%.
Digital LVDS Outputs
The MAX109 provides data in offset binary format to
differential LVDS outputs on four output ports (PortA,
PortB, PortC, and PortD). A simplified circuit schematic
of the LVDS output cells is shown in Figure 5. All LVDS
outputs are powered from the output driver supply
V
CC
O, which can be operated at 3.3V ±10%. The
MAX109 LVDS outputs provide a differential output-
voltage swing of 600mV
P-P
with a common-mode volt-
age of approximately 1.2V, and must be differentially
terminated at the far end of each transmission line pair
(true and complementary) with 100Ω.
Data Out-of-Range Operation
(DORP, DORN)
A single differential output pair (DORP, DORN) is pro-
vided to flag an out-of-range condition, if the applied
signal is outside the allowable input range, where out-
of-range is above positive full scale (+FS) or below
negative full scale (-FS). The DORP/DORN transitions
high/low whenever any of the four output ports (PortA,
PortB, PortC, and PortD) display out-of-range data.
DORP/DORN features the same latency as the ADC
output data and is demultiplexed in a similar fashion, so
that this out-of-range signal and the data samples are
time-aligned.
Demultiplexer Operation
The MAX109’s internal 1:4 demultiplexer spreads the
ADC core’s 8-bit data across 32 true LVDS outputs and
allows for easy data capture in three different modes.
Two TTL/CMOS-compatible inputs are utilized to create
the different modes: SDR (standard data rate), DDR
8-Bit, 2.2Gsps ADC with Track/Hold Amplifier
and 1:4 Demultiplexed LVDS Outputs
18 ______________________________________________________________________________________
Table 1. Timing Adjustments for T/H
Amplifier and Quantizer
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